Valve spring installed height

[RaulAlonso]

I have a set of heads I'm assembling and while setting up the springs I have a few that are .015-.020 off (to high) ,and on my spring pressure gauge(mini gauge in a arbor press) I can not really see a difference in pressure between installed height and +.015-.020. I do not have shims on any of the other valves. installed height is 1.975 and all but 3 are within .010 of that. should i worry about the extra installed height? and shim accordingly or run it with the extra height its hyd. flat tappet app. 135-320lbs

[mag2555]

I would just run the set up as is as long as that added .020" of installed height does not reduce/ eat into the .060" before coil bind spec on those springs you are using.

[David Redszus]

A change in installed height of 0.010" will result in a change in seat FORCE of approx 1.6 lbs and a change in nose
FORCE of 1.6 lbs. Springs are always measured in unit of FORCE, never pressure.

It is highly probable that the variation in installed seat and nose force, from spring to spring, will exceed this value
by a lot.

Your next step is to accurately measure spring installed height since any variance will affect installed spring forces.

[novadude]

A change in installed height of 0.010" will result in a change in seat FORCE of approx 1.6 lbs and a change in nose
FORCE of 1.6 lbs. Springs are always measured in unit of FORCE, never pressure.

It is highly probable that the variation in installed seat and nose force, from spring to spring, will exceed this value
by a lot.

Your next step is to accurately measure spring installed height since any variance will affect installed spring forces.

The force vs pressure thing bugs me too. Force, not pressure. However, you forgot the rocker ratio when talking nose force.

[David Redszus]

A change in installed height of 0.010" will result in a change in seat FORCE of approx 1.6 lbs and a change in nose
FORCE of 1.6 lbs. Springs are always measured in unit of FORCE, never pressure.

It is highly probable that the variation in installed seat and nose force, from spring to spring, will exceed this value
by a lot.

Your next step is to accurately measure spring installed height since any variance will affect installed spring forces.

The force vs pressure thing bugs me too. Force, not pressure. However, you forgot the rocker ratio when talking nose force.

You're right, I did not include the rocker ratio since there is a wide range of ratios and some engines have none at all.

Two issues come to mind.
Nose force has little value except at very low engine rpm. The nose force will change with valve lift and is not maximized at maximum valve acceleration where it is needed. Seat force is critical for sealing and smooth valve closing.

There is a large difference between static forces and dynamic forces. Only one of which matters.
A plot of spring force vs valve force at various lifts and rpms will quickly reveal the problem to be solved.

[David Vizard]

A change in installed height of 0.010" will result in a change in seat FORCE of approx 1.6 lbs and a change in nose
FORCE of 1.6 lbs. Springs are always measured in unit of FORCE, never pressure.

It is highly probable that the variation in installed seat and nose force, from spring to spring, will exceed this value
by a lot.

Your next step is to accurately measure spring installed height since any variance will affect installed spring forces.

Finally someone other than me uses the correct terminology!!!!!
DV

[Roadknee]

A change in installed height of 0.010" will result in a change in seat FORCE of approx 1.6 lbs and a change in nose
FORCE of 1.6 lbs. Springs are always measured in unit of FORCE, never pressure.

It is highly probable that the variation in installed seat and nose force, from spring to spring, will exceed this value
by a lot.

Your next step is to accurately measure spring installed height since any variance will affect installed spring forces.

1.6 lbs per 0.010” equates to a spring rate of 160 lb/in. His springs are probably more than double that.

[BradH]

I had to Google "force vs pressure" as a result of this thread.

[MadBill]

So, should we now move on to discuss lb-ft.(torque) vs. ft-lb (work)?

[hoodeng]

In Smith's book 'Valve mechanisms for high speed engines' he covers what he called 'stab pressures' [his terminology not mine] in reference to what loading the valve train in its entirety is subject to. The Achilles heel that was identified as the most susceptible to distortion was the pushrod [if applicable] there was reference to stab loads being multiples of the installed seat load when a static body is induced into motion.

A spring i use a lot has a spring rate of 6lb@ +.010" lift, getting seat loading's as even as possible i find is more to do with service reference at a later date than the impact of a variance of say 6lb, although given a variance in setup due to shims being .015"minimum i would add to the seat load not subtract.

As to the Pressure/ Force discussion, i fully understand the argument in support of what we refer seat loading as being a 'Force' at a point of contact and not as a 'pressure' exerted in a void , but i do find myself falling into the evil clutches of inadvertently referring to the effect of the valve to seat load as a pressure.

{note to self,be vigilant in conversation, it's force}

Cheers.

[David Redszus]

So, should we now move on to discuss lb-ft.(torque) vs. ft-lb (work)?

Bill, I would very much appreciate if you could explain how and why the same numerical values and units, have different meaning in terms of application. I have never understood the difference and would like to know why the difference does exist.

With regard to spring "pressures", there are proper applications for the term.

The first has to do with valve spring wire stress. If we take the applied spring force (lbs) and divide by spring wire cross sectional area (in^2), we have a spring pressure (lbs/in^2) which is a measure of spring stress. If the spring stress (psi) exceeds the tensile of the material we have material plastic distortion or breakage. Typical values are in the 150,000 psi range and will increase with spring compression.

The second has to do with valve seat pressure which is spring seat force divided by seat contact area.
For a valve seat with major/minor dimensions of 51/48mm and a seat force of 60 lbs, we would have 120 psi seat pressure.

This pressure is what seals the valve to the seat and must be high enough to break through carbon and deposit build up and provide a gas seal.

[MadBill]

This conundrum is yet another nail in the coffin of Imperial vs. Metric, since in the latter system, work is measured in Joules and torque in Newton meters.
I'll save my typing finger via a link re the subject: https://www.macsmotorcitygarage.com/foo ... ifference/

[hoodeng]

The university link to "A dictionary of units of measurement" is now an error 404, but i did find a number of other pages to destroy time over the inane and technically correct. I would have to say the distinction between foot pounds and pounds feet to me is lost in lexical semantics,,but,,,i understand they are correct in their difference.
[In my workshop i won't be screaming WHATTTT! if a miss-reference is used,, i will just add it surreptitiously to the invoice]

I have included a photo of another dictionary i use when lost for words, 480 pages of argument stoppers.

Cheers.

[Kevin Johnson]

The university link to "A dictionary of units of measurement" is now an error 404, ...

https://web.archive.org/web/20180501201 ... index.html

[David Redszus]

This conundrum is yet another nail in the coffin of Imperial vs. Metric, since in the latter system, work is measured in Joules and torque in Newton meters.
I'll save my typing finger via a link re the subject: https://www.macsmotorcitygarage.com/foo ... ifference/

Of all that i have examined, the statement below (from macsmotorcitygarage) makes the most sense to me.

I’ve been retired for 22 years. When I was an engineering student about 60 years ago the Society of Mechanical Engineers decided to call static torque pound-feet, and dynamic torque foot-pounds. Somehow this got lost.

But even this simple definition has been reversed in practice.

In any case, torque is always a measure of force x distance and not of work since the unit of time is not present.